Truncus Arteriosus

What is truncus arteriosus?

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Truncus arteriosus is a congenital (present at birth) defect that occurs due to abnormal development of the fetal heart during the first 8 weeks of pregnancy. The heart begins as a hollow tube, and the chambers, valves, and great arteries develop early in pregnancy. The aorta and pulmonary artery start as a single blood vessel, which eventually divides and becomes two separate arteries. Truncus arteriosus occurs when the single great vessel fails to separate completely, leaving a connection between the aorta and pulmonary artery.

Another congenital heart defect that nearly always occurs with truncus arteriosus is a ventricular septal defect (a hole in the dividing wall (septum) between the two lower chambers of the heart known as the right and left ventricles).

Normally, the aorta and the pulmonary artery are separate. Oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped through the aorta out to the body.

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In truncus arteriosus, oxygen-poor (blue) and oxygen-rich (red) blood mix back and forth through the ventricular septal defect. This mixed blood then flows through the common truncus. From there, some of it will flow through the part of the truncus that becomes the pulmonary artery, and into the lungs. Some of the mixed blood will also go to the part of the truncus that becomes the aorta and continue to the body. The mixed blood that goes to the body does not have as much oxygen as normal, and may cause varying degrees of cyanosis (blue color of the skin, lips, and nail beds).

Truncus arteriosus is uncommon, and affects less than 1% of all cases of congenital heart disease.

What causes truncus arteriosus?

Some congenital heart defects may have a genetic link causing heart problems to occur more often in certain families. Other times this heart defect occurs by chance, with no clear reason for its development.

Why is truncus arteriosus a concern?

The blood that passes through the common truncus has a lower oxygen content than normal. Oxygen-poor (blue) blood from the right ventricle and oxygen-rich (red) blood from the left ventricle mix together before entering the common vessel. Some of this mixed blood will go into the aorta and on to the body, producing some degree of cyanosis (blue color of the skin, lips, and nailbeds).

The pulmonary artery section of the common vessel gets more blood flow than the aorta does because the pressure is lower in the lungs than in the body and it is easier for blood to travel in that direction. If not repaired, the blood vessels in the lungs will become damaged by long-term exposure to the extra blood flow. As the pressure in the blood vessels in the lungs becomes higher, less blood goes to the lungs and more goes to the body. Cyanosis can worsen as blood with lower amounts of oxygen travels to the body.

What are the symptoms of truncus arteriosus?

The following are the most common symptoms of truncus arteriosus. However, each child may experience symptoms differently. Symptoms may include:

Cyanosis

Fatigue

Sweating

Pale skin

Cool skin

Rapid breathing

Heavy breathing

Rapid heart rate

Congested breathing

Disinterest in feeding, or tiring while feeding

Poor weight gain

The symptoms of truncus arteriosus may look like other medical conditions or heart problems. Always consult your child's doctor for a diagnosis.

How is truncus arteriosus diagnosed?

Your child's doctor may have heard a heart murmur during a physical exam. If so, you may have been referred to a pediatric cardiologist for a diagnosis. In this case, a heart murmur is a noise caused by the turbulence of blood flowing through the truncus. Symptoms your child exhibits will also help with the diagnosis.

A pediatric cardiologist specializes in the diagnosis and medical management of congenital heart defects, as well as heart problems that may develop later in childhood. The cardiologist will perform a physical exam, listen to the heart and lungs, and make other observations that help in the diagnosis. The location within the chest that the murmur is heard best, as well as the loudness and quality of the murmur (such as, harsh or blowing) will give the cardiologist an initial idea of which heart problem your child may have. Other tests may include:

Electrocardiogram (ECG). A test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle stress.

Echocardiogram (echo). A procedure that evaluates the structure and function of the heart by using sound waves recorded on an electronic sensor to produce a moving picture of the heart and heart valves.

Cardiac catheterization. A cardiac catheterization is an invasive procedure that gives very detailed information about the structures inside the heart. Under sedation, a small, thin, flexible tube (catheter) is inserted into a blood vessel in the groin, and guided to the inside of the heart. Blood pressure and oxygen measurements are taken in the four chambers of the heart, as well as the pulmonary artery and aorta. Contrast dye is also injected to more clearly visualize the structures inside the heart.

Treatment for truncus arteriosus

Specific treatment for truncus arteriosus will be determined by your child's doctor based on:

Adequate nutrition. Infants may become tired when feeding, and may not be able to take in enough calories to gain weight. Options that can be used to ensure your baby will have adequate nutrition include:

High-calorie formula or breast milk. Special nutritional supplements may be added to formula or pumped breast milk to increase the number of calories in each ounce, thereby allowing your baby to drink less and still consume enough calories to grow.

Supplemental tube feedings. Feedings given through a small, flexible tube that passes through the nose, down the esophagus, and into the stomach, can either supplement or take the place of bottle-feedings. Infants who can drink part of their bottle, but not all, may be fed the remainder through the feeding tube. Infants who are too tired to bottle-feed may receive their formula or breast milk through the feeding tube alone.

Surgical repair. Surgery is usually done within the first few weeks after birth, before the blood vessels in the lungs are overwhelmed by extra blood flow and become damaged.

The operation is done under general anesthesia, and involves the following:

The pulmonary arteries are detached from the common artery (truncus arteriosus) and connected to the right ventricle using a homograft (a section of pulmonary artery with its valves intact from a tissue donor). Occasionally, a conduit (a small tube containing a valve) is used instead of a homograft (human tissue valve).

The ventricular septal defect is closed with a patch.

Care for your child in the hospital

Children will spend time in the intensive care unit (ICU) after a truncus repair.

While your child is in the ICU, special equipment will be used to help him or her recover, and may include the following:

Ventilator. A machine that helps your child breathe while he or she is under anesthesia during the operation. A small, plastic tube is guided into the windpipe and attached to the ventilator, which breathes for your child while he or she is too sleepy to breathe effectively on his or her own. After a truncus repair, children will typically benefit from remaining on the ventilator for several days so they can rest.

Intravenous (IV) catheters. Small, plastic tubes inserted through the skin into blood vessels to provide IV fluids and important medicines that help your child recover from the operation.

Arterial line. A specialized IV placed in the wrist or other area of the body where a pulse can be felt, that measures blood pressure continuously during surgery and while your child is in the ICU.

Nasogastric (NG) tube. A small, flexible tube that keeps the stomach drained of acid and gas bubbles that may build up during surgery.

Urinary catheter. A small, flexible tube that allows urine to drain out of the bladder and accurately measures how much urine the body makes, which helps determine how well the heart is functioning. After surgery, the heart will be a little weaker than it was before, and, therefore, the body may start to hold onto fluid, causing swelling and puffiness. Diuretics may be given to help the kidneys remove excess fluid from the body.

Chest tube. A drainage tube may be inserted to keep the chest free of blood that would otherwise accumulate after the incision is closed. Bleeding may occur for several hours, or even a few days after surgery.

Your child may need other equipment not mentioned here to provide support while in the ICU, or afterwards. The hospital staff will explain all of the necessary equipment to you.

Your child will be kept as comfortable as possible with several different medications; some of which relieve pain, and some of which relieve anxiety. The staff will also be asking for your input as to how best to soothe and comfort your child.

After discharge from the ICU, your child will recuperate on another hospital unit for a few days before going home. You will learn how to care for your child at home before your child is discharged. Your child may need to take medications for a while at home, and these will be explained to you. The staff will give you instructions regarding medications, activity limitations, and follow-up appointments before your child is discharged.

Caring for your child at home

Pain medications, such as acetaminophen or ibuprofen, may be recommended to keep your child comfortable at home. Your child's doctor will discuss pain control before your child is discharged from the hospital.

Often, infants who fed poorly prior to surgery have more energy after the recuperation period, and begin to eat better and gain weight faster. However, high-calorie formulas may be needed for several weeks or months after surgery to help your child catch up growth-wise. Tube feedings may also be helpful until your child is able to feed better.

After surgery, older children usually have a fair tolerance for activity. Your child may become tired easily, and sleep more right after surgery, but, within a few weeks, your child should be fully recovered.

You may receive additional instructions from your child's doctors and the hospital staff.

Long-term outlook

Most children who have had truncus arteriosus surgical repair will live healthy lives. Activity levels, appetite, and growth will eventually return to normal in most children.

Future intervention may be necessary if the pulmonary artery branches were small and do not grow well after surgery. The homograft or conduit connecting the right ventricle to the pulmonary artery may also need to be replaced in the future as your child grows. Surgery in young adulthood is often needed to replace the conduit and/or the valve.

Your child's cardiologist may recommend that antibiotics be given to prevent bacterial endocarditis because of the homograft or conduit.

Regular follow-up care at a center offering pediatric or adult congenital cardiac care should continue throughout life.